Microwave electronic switch



LEW-" March 26, 1957 J. F. ZALESKI 2,786,979

MICROWAVE ELECTRONIC SWITCH 2 Sheets-Sheet 1 Filed March 9, 1954 POWERSUPPLY INVENTOR. JOHN-F. ZALE5K\ March 26, 1957 J. F. ZALESKI 2,786,979

MICROWAVE ELECTRONIC SWITCH Filed March 9, 1954 2 Sheets-Sheet 2 CATHODECATHODE owsz PowEz POWE! SUPPLY SWH'CH swwcu 4 INVENTOR. JOHN F.ZALESK\AT TOKNEY MICROWAVE ELECTRONIC SWITCH John F. Zaleski, Valhalla, N. Y.,assignor to (general Precision Laboratory Incorporated, a corporation ofNew York Application March 9, 1954, Serial No. 415,071

Claims. (Cl. 333-7) This invention relates to electronic switches whichemploy streams of electrical particles as the only moving elements, andmore particularly to electronic switches in which there is interactionbetween a stream of electrical particles and an electromagnetic field.

The present invention uses the principle of electron velocity variationto produce electronic bunching. By this means an electromagnetic fieldis caused to affect an electron stream which in turn is caused to excitea second electromagnetic field. By employing several electron streams orby deflecting a single electron stream the energy of an appliedmicrowave field is caused to appear at a selected one of two or moreoutput wave guide terminals. By appropriate direct-current switching ofthe electron stream generators or electron guns the micro wave energymay be switched between or among outlets, or may be cut ott altogether.

This invention avoids the use of ionizable gases and therefore theswitching speed is not limited by gas ionization or deionization time,but is limited only by the switching speed of a direct-current circuit,which may be made very fast.

In one form of this invention microwave field energy is applied to atuned chamber, causing it to resonate at the microwave frequency. Astream of electrons from an electron gun is passed through the chamberand in passing becomes velocity modulated, causing the electrons tobecome bunched. These bunched electrons are next passed between metalliccharged plates so that the stream is deflected. The stream is thenpassed through a second resonant chamber tuned to resonate at the bunchfrequency. Microwave energy is abstracted from this chamber by an outputguide. By changing the direct-current charge on the plates, thedeflection of the electron stream is changed so that the stream isremoved from the second chamber and applied to a similar third chamber,which resonates and gives up its energy to a second output guide.

By appropriate constructions a number of output chambers and guides canbe, employed, with appropriate switching arrangements to switch theelectron beam with precision to any desired output chamber.

In place of the metallic charged plates for electrostatic deflection ofthe electron stream one or more magnetic solenoid coils may besubstituted for the magnetic deflection of the electron stream.

In another form of this invention an input resonant chamber issandwiched between two output resonant chambers, each provided with itsinput or output hollow waveguide or coaxial line. An electron gun ispositioned on one side of the chambers to project its electron streamthrough all three chambers and another electron gun is positioned on theother side of the chambers to project its electron stream through allthree chambers in the opposite direction. Application of the stream fromone of these guns couples the input microwave line to one output line,and alternatively the stream from the other gun couples the input lineto the other output line.

nited States Patent The time required to convert an electromagneticfield into a velocity varied stream of electrons, to pass this streaminto an output cavity, and to reconvert the stream variations into anoutput electromagnetic field takes little longer than does the passageof the stream of electrons through the device, which is less than onethousandth of a microsecond. Some of the utility of this invention isattributable to this short operation time, because the fastest devicesheretofore available have required times measured in microseconds foroperation.

The employment of this switch as a radar antenna transfer switchprovides one example of use. In the radar art it is general practice toemploy TR tubes and ATR tubes in conjunction with resonant andanti-resonant lengths of guide to provide means for switching a singleantenna between transmitting and receiving circuits, with isolation ofthe disconnected circuit on the order of 30 db. The switch of thepresent invention permits antenna switching from transmitter to receiverwithout the necessity for using resonant or anti-resonant lengths ofwaveguide, and at speeds limited only by direct current circuit speeds.It is therefore possible to reduce the minimum radar echo range to theneighborhood of five feet, instead of'a minimum range measured inhundreds of yards. Moreover, the isolation of the receiver duringtransmission is on the order of db, and may be considered to be infinitefor all practical purposes. This in turn permits the employment ofreally sensitive and highly delicate apparatus in the receiver withoutdanger of injury by leakage from the transmitter. This invention alsoremoves the possibility of receiver injury as a limitation on increaseof transmitter power.

The nature of the electronic switch of this invention is such that notonly do signals suffer no attenuation during passage through the switch,but they may actually undergo amplification of as much as 28 db. Whenthe switch is used as a radar antenna switch the transmitter signal maybe amplified by 14 db and the echo signal may be amplified by 28 dbbefore application to the receiver demodulator, which may in somecircumstances greatly increase the overall sensitivity to echo signals.In addition the size of transmitter required is reduced and/or the radarrange is extended.

The principal purpose of this invention is to provide a high speedelectronic switch, employing electron stream velocity variation, forswitching an input microwave circuit to any one of a plurality of outputcircuits.

Another purpose of this invention is to provide an electronic switchemploying velocity variation of an electron stream eontrolled by anelectrostatic field.

Another purpose of this invention is to provide an electronic switchemploying velocity variation of an electron stream controlled by anelectromagnetic field.

Another purpose of this invention is to provide a threeterminalelectronic switch containing two electron guns alternatively used.

Another purpose of this invention is to provide an electronic device toconnect a microwave transmission line to either of two other microwavetransmission lines without attenuation of microwave energy passingthrough the device.

Another purpose of this invention is to provide an electronic device toswitch microwave energy with concomitant amplification during passagethrough the device.

A further understanding of this invention may be secured from thedetailed description and accompanying drawings, in which:

Figures 1, 2 and 3 depict one form of the microwave electronic switch ofthis invention, Fig. 3 being across section of Fig. 1 on the line 3-3.

Figure 4 represents a circuit for circularly deflecting an electronbeam.

Figure 5 depicts a second form of the microwave electronic switch of theinvention.

Referring now to Fig. 1, one form of microwave electronic switchemploying the principles of this invention contains a conventionalelectron gun in a glass envelope 11, with terminals brought out througha base 12 in the usual manner. The electron gun contains a heater 13,cathode 14, control grid 16 and focusing cylinder 17. The electronstream leaves the focusing cylinder as a compact beam and passes througha smoothing grid 18, smoothing cylinder 19 and grid 21 into a resonantchamber 22; This chamber 22 is made of metal and is sealed to the gunenvelope at 23. The chamber has the form of a short cylinder with acylindrical Wall 24 and end discs 26 and 27. The end 'disc 27 containsthe reentrant tubulation 28 terminated in a grid 29.

The electron stream leaves the resonant chamber 22 by passing throughthe grid 29, then passes between two parallel metal plates 31 and 32having electrical connections 33 and 34 anchored in a surroundingtubular glass envelope 36 which is sealed to the outer surface of theresonant chamber end wall 27. The electron stream is electrostaticallydeflected at either one of two angles as it passes between the plates 31and 32, after which the stream impinges on one of two similar catcherresonant chambers 37 and 38.

The construction of these chambers is exemplified by that of chamber 37,which has a cylindrical Wall 39 and discs 41 and 42, the disc .2 beingprovided with a reentrant tubulation 43. The chamber 37 has an axialinput aperture covered by a grid 44 and an output aperture throughtubulation 43 covered by a grid 46. The electron stream after passingthrough grids 44 and 46 enters an absorption chamber 47 where it isabsorbed in a graphite cup 48. The cup 48 is held in a metal cup 49sealed to the end disc 42 and provided with radiation fins 51. Thepurpose of the absorption chamber 47 is to prevent any electrons afterpassing through chamber 37 from being reflected back through thatchamber, as such fed-back electrons may under some conditions causeself-oscillation. Any type of absorption device may be employed or, insome cases, it may be dispensed with as unnecessary.

The glass envelope 36 is flared at 52 and is joined by an annular seal53 to a conical adapter ring 54 which is in turn sealed to the chambers37 and 38. The construction is shown more clearly in the end view ofFig. 2, the ring 54 being sealed to the outside surfaces of chambers 37and 38. The electron beam space is hermetically sealed and is highlyevacuated in accordance with electronic tube practice.

The resonant chambers 22,37 and 38 are all tuned to the same frequency,and as they are high-Q chambers accurate tuning is highly desirable.Therefore in practice provision is made for final tuning adjustmentafter assembly. One way in which this can be done is by the provision ofa flexible section of the cylindrical wall with V ascrew by which thevolume enclosed by the cavitymay be slightly increased or decreased. Thediaphragm 56, Fig. l, is such a section, adjusted by screw 57. Thechambers 37 and 38 are similarly adjusted by screws 58 and 59, Fig. 2.Other methods of tuning will suggest themselves to one skilled in theart. 1

The input waveguide 61 is coupled to resonant chamber 22'by means of aniris 62, and output waveguides 63 and 64 are attached to chambers 37 and38 and coupled to them by iris openings 66 and 67. In place ofwaveguides coaxial conductors can be used and in place of iris couplingmagnetic loop couplings can be used in accordance with conventionalpractice.

In operation, a source 68 of direct potential is connectedbetween theterminals 33 and 34 of the electrostatic deflection plates 31 and 32,with provision for reversing polarity. This reversal may be eifected atvery high speed by means of conventional electronic tube circuits energyat a selected frequency is applied from a generator to the wave guide 61and the three resonant chambers are tuned to that selected frequency.Switch 69 is placed on terminal 73, making the deflector plate 31positive and 32 negative.

Under these conditions the electron stream from the electron gun issubject, in the space between grids 21 and 29, to potentials of theresonating chamber 22 alternately accelerating and decelerating theelectron passage. That is, the stream is velocity modulated. Afterleaving grid 29 the stream is not further accelerated or decelerated,and its electrons tend to collect in bunches. The greatest bunchingeffect is at a distance from the grid 29 depending upon parametersincluding the cathode-plate potential, and these parameters arepreferably adjusted so that bunching is pronounced at the input grids 44and 44 of the resonant chambers 37 and 38. As the stream of electronspasses between the plates 31 and 32 it'is deflected upward by an angledepending on the potential of source 68. This potential is made of suchamount that the stream is deflected to enter grid 44. Upon entering grid44 the stream produces alternations of potential between grids 44 and 46at the resonant frequency of the chamber 37 setting it into oscillation,and microwave energy is abstracted from it by the waveguide 63. When theswitch 69 is thrown to terminal 74 the electron stream is transferred tocavity 38 and the microwave energy output is thereby switched from guide63 to guide 64.

The construction of the tube depicted in Fig. 1 may be modified toemploy three or more receiving resonant chambers, and by the use of twopairs of electrostatic deflection plates or two sets of electromagneticdeflection coils to direct the electron stream into any selected one ofthe plurality of receiving resonant chambers. These chambers may bearranged in a circle or in any other convenientconfiguration which canbe secured'to the large end of the flared tube 52. The deflectionelements must be excited from an appropriate switching device such asthe sine-cosine potentiometer of Fig. 4. In this figure the'knob 76represents manual or automatic operation of the arm 77 of a cosinepotentiometer 78 and of the arm 79 of a sine potentiometer 81. Bothotentiometers are fed from the same constant potential source 82 and theoutputs are applied to orthogonal plates 83 and 84 of a tube such asthat of Fig. 1. The arms 77 and 79 maybe combined on a single resistancecard. At constant input voltage E, rotation of knob 76 deflects anelectron stream passing through plates 83 and 84 in a circle, andchangeof E changes the stream radially, so that the entire area of theend of the flared tube is availablefor placement of receiving resonantchambers;

In the tube depicted in Fig. 1 the amount of velocity variationoriginated in chamber 22 is controlled by the gun cathode potential, andthe velocity variation together with the distance between grid 29 andgrid 44 control the bunchingefficiency of the tube. A differentarrangement having a more'easily controlled drift distance'and requiringno deflection means, but necessitating the use of two electron guns,isillustrated in Fig. 5.

In Fig. 5 three similar resonant chambers of the reentrant cylinder form, 86, 87 and 88, are positioned in axial alignment. These chambers areconnected by drift tubes 89 and 91 having their ends closed toelectromag netic field energy by grids 92, 93, 9.4 and. 96. Chambers 86and 88 are provided with smoother tubes 97 and 98 closed by grids 99,101, 102 and 103. Two similar electron guns are provided sealed to thesmoother tubes 97 and 98 and axially aligned with them. These guns areenclosed in glass envelopes 104 and 106 and are provided with pin bases107 and 108. The construction of these electron guns is exemplified bythat of the electron gun in envelope 104. This electron gun has ahelical filamentary cathode 109 and a control grid 111 enclosed in afocusing cylinder 112. An absorbent target 113 is made of dissipativematerial such as carbon. Power supplies 114 and 116 are connected to thepins of bases 107 and 108 so as to energize the filaments, apply controlgrid potentials and apply negative potentials to the cathodes relativeto the metallic resonant chamber assembly, which is grounded. Each ofthe two cathode connections for applying cathode-anode potential to theguns is completed through a cathode power switch 117 and 118, forcontrolling the guns. Application of negative potential to a cathodeinitiates the electron stream and interruption of the potentialinterrupts the stream.

Obviously the filament 109 can be enclosed in a cylindrical enclosurehaving an axial aperture, and the end of the cylindrical enclosurefacing the resonant chamber assembly can be coated withelectron-emitting material. The filament then becomes a heater and thecylinder is an indirectly heated cathode.

The three resonant chambers must as a practical matter be tuned afterassembly and while operating. Any of a number of conventional forms oftuning structure may be employed such as that shown in Figs. 1 and 2.Another form is shown in Fig. 5. It uses flexible chamber end disc 119,121 and 123, and screws to adjust the amounts by which the reentrantdrift tube ends project into the chambers. These screws are connectedbetween the outer end discs 124 and 126 and the inner chamber end disc122 and intermediate flanges 127 and 128, which are connected to drifttubes 89 and 91 respectively. The adjustment screws are positioned atseveral points around the periphery of the chamber assembly, one screw129 being shown.

Microwave connections are made to the chambers by means of threerectangular microwave guides 131, 132 and 133, coupling being effectedby hermetically sealed irises 134, 136 and 137. Alternativelyconnections can be made by any other conventional method.

In operation, microwave energy is applied to the middle resonant chamber87 through its input guide 132. The resonant chamber 87 is excited andoscillates at its tuned frequency, which is also the input frequency. Nofield energy can pass through the grids 93 and 94, which behave so faras the field is concerned as if they were solid walls. When the electrongun 104 is energized, gun 106 being left deenergized, an electron beamis generated and passes through focusing tube 97, drift tube 89, drifttube 91, and focusing tube 98 to the right-hand electron gun structure.The filamentary cathode 138 being cylindrical, the electron beam passesthrough it axially and impinges on the carbon block 139, where it isabsorbed. In the passage of the electron beam the several grids 99, 101,92, 93, 94, 96, 102 and 103 have little obstructive effect. However ifdesired these grids can be made very coarse or even omitted withoutgreatly increasing the microwave field leakage. As the electron beampasses through resonant chamber 87 it is velocity modulated by the fieldtherein, so that the electrons entering chamber 88 are bunched andgenerate resonation therein. Energy is abstracted from this chamber byguide 133.

The excitation of gun 104 thus elfectively couples chamber 87 to chamber88 so that the energy applied through guide 132 is effectivelyabstracted through guide 133. In general it is easy to employ suchparameters as to effect zero attenuation in the circuit from the inputguide to the output guide. Moreover, at selected parameter valuesconsiderable voltage and/or power amplification takes place so that theoutput voltage and/or power is" greater than at the input.

The structure is symmetrical and when excitation is removed from gun 104and applied to gun 106 the cathode beam is passed from right to left andis absorbed at target 113. The beam is velocity modulated in chamber 87and gives up its energy to chamber 86, from which it is abstracted byguide 131.

Any one of the three chambers, 86, 87 and 88, can be excited and serveas the input chamber, with either of the other two chambers serving asthe output chamber, provided only that an electron beam passes firstthrough the inputchamber and second through the output chamber. It isnot necessary that the chamber serving as input when one of the electronguns is used also serve as input when the other electron gun is used.For example, when the gun 104 is used chamber 87 may be the inputchamber and chamber 88 the output chamber. When gun 104 is switched offthe gun 106 is switched on the chamber 88 may be used as the inputchamber and chamber 86 as output chamber. There are obviously severalpossible cases: when gun 104 is used chamber 86 may be the inputchamber, with either chamber 87 or chamber 88 the output chamber, orchamber 87 may be the input chamber and chamber 88 the output chamber.

It is in addition possible under some conditions to employ two inputcircuits simultaneously or two output circuits simultaneously in thismicrowave switch.

What is claimed is:

l. A microwave switch comprising, an input microwave chamber and atleast a pair of output microwave chambers, each of said chambers beingresonant at the same microwave frequency, passageways extending indiiferent directions interconnecting said input chamber with each ofsaid output chambers, said passageways be ing .impervious to microwaveenergy at said frequency but pervious to an electron stream, electrongun means for projecting an electron stream through respectivepassageways to intercouple the microwave energy in said input chamberinto selected ones of said output chambers, switch actuated means foraltering the direction of said electron stream in said differentdirections selectively to intercouple selected ones of said outputchambers with said input chamber, and microwave transmission circuitscoupled to each of said microwave chambers.

2. A microwave electronic switch comprising, an input microwave resonantchamber and a plurality of output micnowave resonant chambers, means forapplying a microwave field .to said input chamber, electron gun meansfor projecting an electron stream through said input chamber wherebysaid electron stream is velocity modulated by the field excited in saidinput chamber, switch means for selectively directing said velocitymodulated electron stream into selected ones of said output chambers,and means for abstracting microwave energy from said output chambers.

3. A microwave electronic switch comprising, an input microwave resonantchamber and a plurality of output microwave resonant chambers,passageways interconnecting said input chamber and respective ones ofsaid output chambers, means for rendering said passageways impervious tothe transmission of microwave field energy, means for applying amicrowave field to said input chamber, electron gun means projecting anelectron stream through said input chamber whereby said electron streamis velocity modulated by the field excited in said input chamber, switchmeans for varying the direction of said velocity modulated electronstream through said passageways into alternately selected ones of saidoutput chamhers, and means for abstracting microwave energy from saidoutput chambers.

4. -A microwave electronic switch comprising, an input microwaveresonant chamber, a pair of output microwave resonant chambers, a firstpassageway interconnecting said input chamber and one of said pair ofoutput chambers, a second passageway interconnecting said input chamberand the other of said pair :of, output chambers, means'for rendering'said passageways impervio to the transmission of microwave fieldenergy, means for applying a microwave field to said ,input chamber,electron gun means proiecting an electron. Stream through said inputchamber whereby said electron stream is velocity modulated by the fieldexcited in said input chamber, means for selectively projecting saidvelocity modulated electron beam through said first and secondpassageways into said one or the other of said output chambers, andmeans for abstracting microwave energy from said output chambers.

5. A microwave switch for transferring microwave energy between one oranother pair of three microwave circuits comprising, three microwavechambers resonant at the same frequency, means coupling said threemicrowave circuits to respective ones of said three microwave chambers,passageways interconnecting said chambers, said passageways beingnonconductive of microwave electromagnetic field energy but permittingpassage of. an electron stream, electron gun means for passing anelectron stream through said passageways, and means for switching saidelectron stream from travel between one pair of said three chambers totravel between another pair of said three chambers.

6. A switch for transferring microwave energy from an input microwavecircuit 'to any one of a plurality of output microwave circuitscomprising, an input microwave resonant chamber connected for excitationby said input microwave circuit, a plurality of output microwaveresonant chambers each connected to a respective one of said pluralityof output microwave circuits for the excitation thereof, passagewaysconnecting said input microwave resonant chamber to each of said outputmicrowave resonant chambers, said passageways having high impedance tothe passage of microwave electromag'-" netic field energy but allowingthe passage of electrons, an electron gun positioned vto pnoject anelectron stream through said input microwave resonant chamber, means forselectively controlling the direction of said electron stream afterpassage through said input microwave resonant chamber to direct itspassage through a selected one of said passageways and into a selectedone of said output microwai e resonant chambers 7. A switch inaccordance with claim 6 in which said meansior controlling'the directionof the electron stream is electrostatic.

8. A microwave switch comprising, three resonant chambers axiallyaligned including a central input chamber .flankedoneach side by anoutput chamber, an electron-beam gun connected axially to each of saidoutput chambers for directing an electron beam axially of said chambersandthereby transferring microwave energy from said input chamber to saidoutput chambers and switch means for selecting one or the other of saidguns.

9. A microwave switch comprising, three resonant chambers axiallyaligned including a central input chamber flanked on each side by anoutput chamber, microwave transmission circuits respectively coupled toeach of said resonant chambers, passageways interconnecting saidchambers, said passageways having very high impedance to passage ofelectromagnetic field energy but transmitting an electron stream, afirst electron gun connected to one of said output chambers andpositioned to direct a stream of electrons through said chambers andsaid passageways in one direction, a second electron gunoonnected to theother output chamber and positinned to direct a stream of electronsthrough said chambets and said passageways in the opposite direction,and means for selecting and alternately operating said electron guns.

10. A microwave switch comprising, three microwave chambers resonant atthe same frequency positioned in axial alignment and provided withinterconnecting passageways therebetween, means in each of saidpassagewalys peivious to an electron stream for preventing the passageof elcctnomagn'ctic'field energy therethrough, an electron gun connectedto one end chamber positioned to direct a stream of electrons throughsaid chambers and said passageways in one direction, a second electrongun connected to the other end chamber positioned to direct a streamofelectrons through said chambers and said passageways in the oppositedirection, means for alternately energizing said electron guns, andmicrowave transmission circuits connected to each of said chambers.

References Cited in the file of this patent UNITED STATES PATENTS

